Continous analyzer of volatile organic compounds, device and method for continuously assessing the quality of inside ambient air and use of said device for monitoring a ventilation installation

ABSTRACT

The present invention concerns a continuous analyser of volatile organic compounds ( 10 ) comprising a circuit ( 18 ) for the sequential processing of air such that the air is drawn in by a pump ( 17 ) through a filter ( 11 ) and scanned by a first sensor ( 15 ) for CO/VOC and the second sensor ( 16 ) for H 2 O, either directly along a first pathway, or after passing through a cartridge ( 12 ) for retaining organic species along a second pathway; the switch over from one to the other of these two pathways being assured by an electric valve ( 13 ) controlled by a sequencer ( 14 ).  
     The present invention also concerns a device and a method for continuously evaluating the quality of interior ambient air.

DESCRIPTION

[0001] 1. Technical Field

[0002] The present invention concerns a continuous analyser of volatileorganic compounds (VOCs), a device and method for continuouslyevaluating the quality of interior ambient air and a use of this devicefor controlling a ventilation unit.

[0003] 2. State of the Prior Art

[0004] Different parameters may be used to characterise the quality ofinterior ambient air, and particularly the concentrations in H₂O, CO₂,CO, NO_(x), and VOC. If each of these compounds is successivelyanalysed, one has:

[0005] H₂O: The hygrometry and the gravimetric concentration in waterare recognised comfort factors. They are also, like CO₂, indicators ofhuman presence but a lot less precise, given the great variability inthe natural humidity levels in air, and the low emissions linked tohuman presence in comparison to the high levels of ambient air.

[0006] CO₂: Carbon dioxide is not really considered as a pollutant, butit is an excellent indicator of human presence in service sectorpremises. It is also a good indicator of poor ventilation in residentialpremises, in particular when cooking equipment or extra heating devicesare being used.

[0007] CO: Carbon monoxide is a pollutant whose presence in servicesector premises is essentially due to the intake of polluted air fromthe exterior, faulty combustion or even tobacco smoke. In residentialpremises it is responsible for a considerable number of mortal accidentseach year due to faulty combustion devices or devices not connected tosmoke exhaust ducts.

[0008] NO_(x): Nitrogen oxides may be represented by the dioxide NO₂,which is the most noxious and the only oxide concerned by externalambient air regulations. In service sector premises, the presence ofNO_(x) is essentially due to the intake of polluted air from theexterior.

[0009] VOC: The term Volatile Organic Compound covers a considerablenumber of compounds whose noxiousness is very variable. Among these,formaldehyde (HCHO) is chosen as the indicator; it is a product of thedegradation of materials, frequently emitted in the interior of rooms,irritant to the mucous membranes and whose long term toxicity is nowrecognised.

[0010] These different compounds may be used to establish an air quality“index”.

[0011] However, using specific analysers with high metrologicalperformance is out of the question, mainly for cost reasons. In fact, asemi-quantitative determination with good reliability is acceptable.

[0012] A first aim of the invention is therefore a continuous analyserof volatile compounds. A further aim is a device and a method forcontinuously evaluating the quality of interior ambient air, which isnot very bulky, easy to use and maintain, of reasonable cost, andcapable of rendering an air quality index determined from pollutantlevels and their relative noxiousness; enabling the five compoundsdefined above to be quantified in a reliable and selective manner, inreal time, using commercially available micro-sensors.

DESCRIPTION OF THE INVENTION

[0013] The present invention concerns a continuous analyser of volatileorganic compounds, characterised in that it comprises:

[0014] a measuring module comprising a first CO/VOC sensor and a secondH₂O sensor,

[0015] a sequential processing circuit for air comprising:

[0016] a filter

[0017] a cartridge for the selective retention of volatile organiccompounds arranged on a first pathway in parallel with a second directpathway

[0018] an electric valve controlled by a sequencer, which assures thefirst pathway—second pathway commutation

[0019] a pump located downstream of the sensors in such a way that theair to be analysed is drawn in through a filter and is transferredtowards the CO/VOC and H₂O sensors either directly, or after passingthrough the cartridge.

[0020] a circuit for processing the signals coming from the sensors andthe sequencer, enabling the following three parameters to be obtained:

[0021] the water content in the air

[0022] the CO content in the air, on a sample with the VOCs removed

[0023] the VOC content, by calculating the difference of the signalsobtained with the help of the CO/COV sensor when the air to be analysedis transferred towards this sensor, either along the first pathway oralong the second pathway.

[0024] The present invention also concerns a device for continuouslyanalysing the quality of interior ambient air comprising this type ofcontinuous analyser of volatile compounds, in which the measuring modulealso comprises sensitive elements of sensors for NO₂ and CO₂, and inwhich the sequential processing circuit for the air drawn in by the pumpthrough the dust filter initially scans the third sensor for NO₂ and thefourth sensor for CO₂, before being transferred towards the first sensorfor H₂O and the second sensor for CO/VOC along the first or secondpathway.

[0025] Advantageously, the first, the second and the third sensors aremetal oxide chemical micro-sensors. The pump is a membrane pump.

[0026] The present invention also concerns a method for continuouslyanalysing the quality of interior ambient air, implementing theaforementioned device, and which comprises the following stages:

[0027] the calibration curve for each of the sensors for measuringdifferent compounds: H₂O, CO/VOC, NO₂ and CO₂ is determined.

[0028] the influence of the majority interfering compounds is correctedby calculation.

[0029] the output signal from each sensor is transposed into measuredcompound concentration, while taking account of its calibration curve.

[0030] a quality index for each compound measured is determined byreferring to an evaluation grid that gives an index value for eachcompound as a function of different thresholds limits for theconcentrations of compounds, in reference to health data.

[0031] an overall index of the quality of the air is obtained as afunction of the different compound indexes obtained.

[0032] The preceding device may be used advantageously for controlling aventilation unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 illustrates the device of the invention.

[0034]FIG. 2 illustrates the response curve for sensor 20.

[0035]FIG. 3 illustrates the calibration curve for sensor 16.

[0036]FIG. 4 illustrates a measuring sequence.

[0037]FIG. 5 illustrates the exploitation of the output signals fromsensors 15 and 16.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0038] As illustrated in FIG. 1, the continuous analyser of VolatileOrganic Compounds 10 successively comprises:

[0039] processing circuit for air comprising:

[0040] a filter 11, which may be a coarse dust filter

[0041] a cartridge 12 for the selective retention of volatile organiccompounds arranged on a pathway 2 in parallel with a direct pathway 1.

[0042] an electric valve 13 controlled by a sequencer 14, which assuresthe first pathway—second pathway commutation

[0043] a first sensor for CO/VOC 15 and a second sensor for H₂O 16.

[0044] a pump 17, which may be a membrane pump.

[0045] a circuit 18 for processing the signals coming from the sensors15 and 16 and the sequencer 14.

[0046] The air to be analysed is drawn in by the pump 17 through thefilter 11 and is transferred to the CO/VOC 15 and H₂O sensors, eitherdirectly, or after going through the cartridge 12; the sequentialcommutation being assured by the electric valve 13.

[0047] The pump 17, which enables the air to be sampled, is placeddownstream of the analysis circuit in such a way as to avoid anycontamination or retention of species.

[0048] The analyser of the invention therefore comprises two main parts:

[0049] a measuring module, which comprises the sensitive elements of thesensors CO/VOC 15 and H₂O sensors, supply and measuring circuits and asequential processing circuit of the sampled air.

[0050] a module 18 for processing and exploiting the signals.

[0051] The device for continuously evaluating the quality of interiorambient air according to the invention, illustrated in FIG. 1, comprisesall of the elements of the analyser 10 of the invention, as defined hereabove. It moreover comprises a third sensor for NO₂ 20 and a fourthsensor for CO₂ 21 arranged between the filter 11and the pathways 1 and2.

[0052] The method for continuously evaluating the quality of interiorambient air according to the invention, implementing the device definedhere above, comprises the following stages:

[0053] the calibration curve for each of the sensors 15, 16, 20 and 21for measuring different compounds: H₂O, CO/VOC, NO₂ and CO₂ isdetermined.

[0054] the influence of the majority interfering compounds is correctedby calculation.

[0055] the output signal from each sensor is transposed into measuredcompound concentration, while taking account of its calibration curve.

[0056] a quality index for each compound measured is determined byreferring to an evaluation grid, such as that illustrated by way ofexample in Table 3, which gives an index value for each compound as afunction of different thresholds limits for the concentrations ofcompounds, referring to health data.

[0057] an overall index i_(global) of the quality of the air is obtainedas a function of the different compound indexes obtained thereof.

EXAMPLE OF AN EMBODIMENT

[0058] In an example of an embodiment, the sensors 15, 16 and 20 forCO/VOC, H₂O and NO₂ used are commercially available metal oxide chemicalmicro-sensors. This type of sensor is made up of a sensitivesemi-conductor element, usually based on tin oxide SnO₂, heated to itsoptimal operating temperature by a heating element, and whose electricalcharacteristics vary as a function of the presence in the ambient air ofgaseous compounds. The sensitive element is the focus point forabsorption—desorption and oxidation—reduction phenomena for which theequilibria are determined principally by the temperature. Theelectronics of such a sensor are very simple.

[0059] The sensor 21 for CO₂ is an infrared (IR) sensor. In fact, CO₂has the property of absorbing infrared radiation with an absorptionmaximum between 4000 nm and 4400 nm. For a given geometry of themeasuring cell, the radiation absorption is directly linked to theconcentration in CO₂ (Beer—Lambert law). This sensor 21 could also be achemical micro-sensor.

[0060] Among the different types of possible sensors, we have retainedby way of example the following sensors 15, 16, 20, 21:

[0061] CO/VOC : FIGARO TGS 2620 sensor

[0062] H₂O : FIGARO TGS 2180 sensor

[0063] NO₂ : FIGARO TGS 2105 sensor

[0064] CO₂ : SAUTER IR sensor/type EGQ 220 F001

[0065] The sensitive elements of sensors 20 and 21 for NO₂ and CO₂ maybe arranged on a support and be exposed directly to the ambient airsampled via the membrane pump.

[0066] The sensor 21 for CO₂ is integral with its electronics and isused as provided by the supplier after having been removed from itsprotective casing for reasons of bulk.

[0067] The sensors 15 and 16 for CO/VOC and H₂O are arranged under acover that makes it possible to scan alternately, either directly by theambient air, or after passing through the cartridge 12.

[0068] The selective retention cartridge 12 for volatile organiccompounds may be obtained by using potassium permanganate.

[0069] In fact, aldehydes, ketones and alcohols react with potassiumpermanganate and are fixed by oxidation, in a quantitative manner;benzenic compounds are retained, a priori, by absorption. The flow ofair to be purged must be low in order to ensure sufficient contact timefor complete trapping, and in practice a flow of 0.3 l/min and acartridge of 200 mm may be used. A lower flow rate makes it possible toreduce the dimensions of the cartridge without affecting its autonomy.Activated aluminium oxide (alumina Al₂O₃) in microporous beads of 2 mmto 5 mm diameter is used as a support for the active compound comprisingpotassium permanganate (KMnO₄). In order to obtain a preparation of 100g, one very simply achieves the impregnation by immersing 100 g ofalumina in an acidified aqueous solution (H₂SO₄ 10⁻²N) at 60 g/l ofpotassium permanganate. After spin drying, the alumina beads are driedat 60-70° C. for around 4 hours and conserved shielded from air, thistreatment making it possible to obtain an alumina containing 5% byweight of KMnO₄. 100 g of this preparation enables 6 cartridges of 200mm/diameter 20 mm to be filled.

[0070] The pump 17 may be a WISA type membrane pump used in gasanalysers, separated from the sensors for reasons of bulk; but it mayalso be a smaller pump that can easily be fitted into the measurementbox.

[0071] The duration of the cycle of the control signal from electricvalve 13, supplied by the sequencer 14, may be chosen between 30 secondsand three hours, for example 5 minutes.

[0072] The circuit 18 for processing the output signals delivered by thesensors 15, 16, 20, 21 is achieved using an AOIP 70 acquisition unitwith its pathways connected to a PC type computer; the mathematicalprocessing of the signals is carried out using EXCEL type software. Itis also possible to use microprocessors integrated in the device of theinvention.

[0073] In this example of an embodiment, the following measurements weremade.

[0074] Measurement of Nitrogen Dioxide (NO₂)

[0075] The measurement was carried out by exposing the sensor 20 for NO₂to the flow of sampled air.

[0076] As illustrated in FIG. 2, the sensor 20 offered a response to thenitrogen dioxide within a relatively narrow concentration field (0 to200 ppb), but appropriate to the concentrations encountered in the areasconsidered, with quite good selectivity, thus allowing the signal to beexploited directly.

[0077] The impact of the CO on the measurement of the NO₂, effective forhigh CO/NO₂ concentration ratios (greater than 100), could bedisregarded without leading to significant errors.

[0078] Measurement of the Humidity (H₂O)

[0079] The measurement of H₂O was carried out using sensor 16, whichoffers good sensitivity and good selectivity to water; its response islinked to the gravimetric concentration in water (expressed in mass/m³or in ppm) and not the relative humidity of the air.

[0080] CO, CO₂, NO_(x) and VOCs do not influence the measurement in theareas concerned by ambient air.

[0081] The response of this sensor 16, illustrated in FIG. 3, was usednot only for measuring the water content but also to correct theinfluence of this water content on the response to CO and to VOCs of thesensor 15.

[0082] Associated Measurements of CO, H₂O and VOCs

[0083] The concentrations of CO, H₂O and VOCs were measured usingsensors 15 and 16.

[0084] The evaluation of the concentrations of CO and Volatile OrganicCompounds (VOCs) was carried out using the multi-pollutant sensor 15,which offers good sensitivity to VOCs but requires a correction for theinfluence of the water concentrations, carried out using the secondsensor 16, specific to water.

[0085] In interior spaces, VOCs are present at very low concentrationscompared to the levels of potentially interfering compounds such as COor H₂O, which makes the corrections by purely mathematical route veryuncertain. This difficulty is overcome by carrying out a selectivetrapping of VOCs using the cartridge 12, upstream of sensor 15, and byalternately introducing purged air and the air to be analysed into thissensor 15. The major interfering agents are not trapped, and thedifferences in the signals makes it possible to obtain, with goodsensitivity, the concentration of VOCs.

[0086] The ranges concerned are as follows:

[0087] H₂O: 5000 to 25000 ppm

[0088] CO: 0 to 25 ppm

[0089] Total VOC: several tens of ppb to 1 ppm.

[0090] By calculating differences in the stabilised signals during eachsequence, it is possible to obtain the concentration of the maskedcompound while at the same time being able to disregard theconcentrations of interfering compounds as well as drifts from zero ofthe sensor.

[0091] The two associated sensors 15 and 16 thus make it possible,according to the signal sampling period, to obtain the following threeparameters with good accuracy:

[0092] the water concentration of the ambient air

[0093] the CO concentration of the ambient air on a sample cleared ofVOCs

[0094] the VOC concentration, by calculating the difference in onesignal and another.

[0095] The air sampled using pump 17 was thus introduced into the twosensors 15 and 16, either directly or after passing through thecartridge 12 as illustrated in FIG. 4. 5 minute sequences were chosen.

[0096] The raw signals delivered by these sensors 15 and 16 were sampledafter stabilisation, in the following manner:

[0097] Pathway 1 (ambient air)

sensor 16

measurement of ambient H₂O

[0098] Pathway 2 (cartridge)

sensor 15

measurement of ambient CO (freed of trapped VOCs)

[0099] (Pathway 1—pathway 2)

measurement of trapped VOCs.

[0100] The signal sampling phases are illustrated in FIG. 5, which showsa typical evolution of signals during a test.

[0101] Measurement of CO₂

[0102] The measurement was carried out using the sensor 21. Thisinfrared sensor, removed from its protective casing, was integratedwithout any modification to the device. This sensor has good responselinearity in its measuring range (0 to 2000 ppm), and good sensitivity.

[0103] To process the output signals from the sensors, the followingcalibration curves were considered:

[0104] Nitrogen Dioxide NO₂/Sensor 20

[0105] The calibration curve is of the type:

[NO₂ ]=a E ^((n))

[0106] where: [NO₂] represents the concentration expressed in ppb and Erepresents the signal from the sensor (in volts).

[0107] Gravimetric Concentration in Water (H₂O)/Sensor 16 “Pathway 1”

[0108] The equation for the calibration curve for sensor 16 is of thetype:

H₂O_(in ppm) =b. (E−E ₀)² +c. (E−E ₀)+d

[0109] Where: E represents the raw voltage delivered by the sensor (involts), and

[0110] E₀ represents the base voltage of the sensor.

[0111] Carbon Monoxide (CO)/sensor 15 “Pathway 2”

[0112] The equation for the calibration curve for the sensor 15vis-à-vis CO is a polynomial of the second degree of the type:

CO_(in ppm) =e. [E−E ₀ −E _((H2O))]² +f. [E−E ₀ −E _((H2O)) ]+g

[0113] Where: E represents the raw voltage delivered by the sensor 2620(in volts),

[0114] E₀ represents the base voltage of the sensor 15.

[0115] E_((H2O)) represents the correction for the influence of thewater concentration on the sensor 15, from the concentration deliveredby the sensor 16.

[0116] Formaldehyde and Volatile Organic Compounds Expressed as“Formaldehyde Equivalents”/Sensor 15 “Pathway 1—Pathway 2”

[0117] Among the major VOCs in polluted ambient air, the cartridge 12quantitatively traps the following compounds and families of compounds:

[0118] formaldehyde and other aldehydes

[0119] ketones (acetone, etc.)

[0120] alcohols (methanol, ethanol, etc.)

[0121] benzenic compounds.

[0122] All of these compounds have a recognised toxicity and the sensor15 has similar sensitivity to them. Among these pollutants, formaldehydeturns out to be in the majority in interior premises and it is all ofthese “undesirable” VOCs taken together that is expressed as“formaldehyde equivalents”.

[0123] The CO (and alkanes), present in the air at concentrations thatcan reach several ppm, is not trapped by the cartridge 12.

[0124] CO, which is toxic, is measured during the sequence correspondingto pathway 2. The measurement of CO integrates the possible presence ofalkanes. If these compounds are present, the measurement is carried outby excess; this constitutes an asset by allowing the device to react tothe presence of methane, in the event of a leak of natural gas forexample.

[0125] For each response level, the averages in pathway 1 and pathway 2are calculated by eliminating the stabilisation phases (around 1 minutebefore and after each commutation).

[0126] For the sensor 15, one has:

[0127] Pathway 2 (trapping) : 0.5×[average (t₀+7 to t 0+9)+average(t₀+17 to t₀+19)] (average of signals from “pathway 2” sequencespreceding and following a “pathway 1” sequence).

[0128] Pathway 1 (direct passage) : average (t₀+12 to t₀+14)

[0129] For the sensor 16, one has:

[0130] Pathway 2 (trapping): 0.5×[average (t₀+7 to t₀+9)+average (t₀+17to t₀+19)] (average of signals from “pathway 2” sequences preceding andfollowing a “pathway 1” sequence).

[0131] Pathway 1 (direct passage) average (t₀+12 to t₀+14).

[0132] The influence of water concentration variations in the sensor 15is corrected very simply by assigning the difference in the signals“pathway 1—pathway 2”, measured on sensor 16, a coefficient Srepresenting the ratio of sensitivities respectively of these twosensors to water, in other words the ratio of the slopes of the tworesponse curves in a humidity range going from 5000 to 25000 ppm.

[0133] The responses from sensors 15 and 16 (raw differential voltagesin volts) in the extreme water content ranges encountered in exteriorair are given in Table 1 at the end of the description. The equation forthe variation curve (assimilated to a straight line) of this ratio as afunction of the water concentration is: Coefficient S=2.10⁻⁵ [H₂O].

[0134] The variations in the water concentrations at the level of sensor15, downstream of cartridge 12, are between 0 and ±6000 ppm; a fixedratio of 1.67 is thus retained between the raw voltages delivered by thesensors 15 and 16 for a same water content.

[0135] The value of 1.67 corresponding to the maximum water contentdifference is retained preferentially to an average coefficient, sinceit enables a better correction matching in so far as only highdifferences have a notable impact on the results. One thus obtains aftercorrection of the response of the water concentration from sensor 15:

VOC (in mg/m³ of HCHO)=K ₁×(Δ(V 1−V 2)₂₆₂₀−1.67×Δ(V 1−V 2)₂₁₈₀)

[0136] Where K₁ is the slope of the response to VOCs of the sensor 15.

[0137] If the second term enables the response to water of sensor 15 tobe corrected, the difference “pathway 1−pathway 2” of the first termenables the response of this sensor to the CO not trapped by thecartridge 12 to be corrected and to allow any drifts from zero of thesensor 15 over time to be disregarded.

[0138] A calibration is carried out by injecting and vaporising knownquantities of HCHO in a 37% aqueous solution; table 2 at the end of thedescription shows values of signals after the treatment described above.The calibration curve is a straight line in a concentration rangebetween 0 and 6 mg/m³.

[0139] Carbon Dioxide/Sensor 21

[0140] The equation for the calibration curve is of the type:

CO₂ in ppm=a×E+b

[0141] in which E represents the signal expressed in volts (1-10 V for0-2000 ppm).

[0142] Establishing an Air Quality Index

[0143] Various approaches for establishing such an index may beenvisaged; one solution consists in comparing the measured concentrationof each of the selected compounds: H₂O, CO, NO₂, HCHO, CO₂ at differentthresholds, as in the grid in Table 3.

[0144] The concentration levels that could be attained by each of theselevels are broken down into 10 classes, established either fromregulatory thresholds, if they exist, or from the recommendations of theWorld Health Organisation for the protection of health and eachconstituting an elementary index.

[0145] The overall index is represented by the highest index of theelementary indices corresponding to each of the selected compounds.

[0146] An example of a CO index is as follows: Regulatory limit inworking atmospheres: 50 ppm over a period of 8 h.

[0147] WHO recommendations:

[0148] 60 mg/m³ (≈50 ppm) during 30 minutes

[0149] 30 mg/m³ (≈25 ppm) during 1 hour

[0150] 10 mg/m³ (≈5 ppm) during 8 hours.

[0151] Maximum retained for the index:

[0152] 20 ppm (23 mg/m³

index 10).

[0153] In the same way, an index 10 corresponds to:

[0154] 1 mg/m³ of VOC expressed in HCHO equivalents (0.8 ppm at 20° C.)

[0155] 200 μg/m³ of NO₂ (109 ppb at 20° C.)

[0156] 2000 ppm of CO₂ (3667 mg/m³) TABLE 1 TGS 2620 H₂O in ppm signalTGS 2180 signal Ratio 2500 0.1938 0.1194 1.623 5000 0.3750 0.2275 1.6486000 0.4440 0.2676 1.659 7000 0.5110 0.3059 1.670 8000 0.5760 0.34241.682 9000 0.6390 0.3771 1.695 10000 0.7000 0.4100 1.707 11000 0.75901.4411 1.721 12000 0.8160 0.4704 1.735 13000 0.8710 0.4979 1.749 140000.9240 0.5236 1.765 15000 0.9750 0.5475 1.781 16000 1.0240 0.5696 1.79817000 1.0710 0.5899 1.816 18000 1.1160 0.6084 1.834 19000 1.1590 0.62511.854 20000 1.2000 0.6400 1.875 22000 1.2760 0.6644 1.921 25000 1.37500.6875 2.000

[0157] TABLE 2 HCHO μg/m³ Signal in volts 0 0.0064 28.5 0.0118 28.50.0113 47.5 0.0168 47.5 0.0153 95 0.225 142.5 0.241 190 0.301 237.50.359 237.5 0.347

[0158] TABLE 3 CO level HCHO level NO₂ level CO₂ level mg/m³ μg/m³ Indexμg/m³ Index ppm Index <1 <50 0 <20 0 <650 0 1 to 2 50 to 75 1 20 to 40 1650 to 800 1 2 to 4  75 to 100 2 40 to 60 2 800 to 950 2 4 to 8 100 to150 3 60 to 80 3  950 to 1100 3  8 to 10 150 to 200 4  80 to 100 4 1100to 1250 4 10 to 12 200 to 300 5 100 to 5 1250 to 1400 5 12 to 14 300 to400 6 120 to 6 1400 to 1550 6 14 to 16 400 to 600 7 140 to 7 1550 to1700 7 16 to 18 600 to 800 8 160 to 8 1700 to 1850 8 18 to 20  800 to1000 9 180 to 9 1850 to 2000 9 CO > 20 >1000 10  >200 10  >2000 10 

1. Continuous analyser of volatile organic compounds characterised inthat it comprises: a measuring module comprising a first CO/VOC sensor(15) and a second H₂O sensor (16), a sequential processing circuit forair comprising: a filter (11) a cartridge (12) for the selectiveretention of volatile organic compounds arranged on a first pathway (12)in parallel with a second direct pathway (11) an electric valve (13)controlled by a sequencer (14), which assures the first pathway—secondpathway commutation a pump (17) located downstream of the sensors (15,16) in such a way that the air to be analysed is drawn in through afilter (11) and is transferred towards the CO/VOC (15) and H₂O (16)sensors either directly, or after passing through the cartridge (12) acircuit (18) for processing the signals coming from the sensors (15, 16)and the sequencer (14), enabling the following three parameters to beobtained: the water concentration of the air the CO concentration of theair, on a sample with the VOCs removed the VOC concentration, bycalculating the difference in signals obtained using the CO/VOC sensor(15) when the air to be analysed is transferred towards this sensoreither along the first pathway or along the second pathway.
 2. Devicefor continuously analysing the quality of interior ambient aircomprising a continuous analyser of volatile compounds according toclaim 1, in which the measuring module also comprises sensitive elementsof sensors for NO₂ (20) and CO₂ (21), and in which the sequentialprocessing circuit for the air drawn in by the pump through the filter(11) initially scans the third sensor (20) and the fourth sensor (21)before being transferred towards the first sensor (15) and the secondsensor (16) along the first or second pathway.
 3. Device according toclaim 2, in which the first, the second and the third sensors (15, 16,20) are metal oxide chemical micro-sensors.
 4. Device according to claim2, in which the pump (17) is a membrane pump.
 5. Method for continuouslyanalysing the quality of interior ambient air, implementing the deviceaccording to any of claims 2 to 4, and which comprises the followingstages: the calibration curve for each of the sensors (15, 16, 20, 21)for measuring different compounds: CO/VOC, H₂O, NO₂ and CO₂ isdetermined. the influence of the majority interfering compounds iscorrected by calculation. the output signal from each sensor istransposed into measured compound concentration, while taking account ofits calibration curve. a quality index for each compound measured isdetermined by referring to an evaluation grid that gives an index valuefor each compound as a function of different thresholds limits for theconcentrations of compounds, referring to health data. an overall indexof the quality of the air is obtained as a function of the differentcompound indexes obtained thereof.
 6. Use of the device according to anyof claims 2 to 4 for controlling a ventilation unit.